1. Field of the Invention
The present invention relates to a method of producing a sesamol formic acid ester (hereinafter referred to as sesamyl formate) with a low by-product yield of heliotropic acid, and to a method of producing sesamol by conducting hydrolysis or alcoholysis of the ester.
2. Background Art
Sesamolxe2x80x943,4-(methylenedioxy)phenolxe2x80x94is a compound in the form of white crystals (melting point 65.5xc2x0 C.) having a phenol odor, and serves as an important starting material for producing pharmaceuticals such as hypotensive agents. Sesamol also finds uses such as antioxidants, antibacterial agents, herbicides, and cosmetics.
Conventionally, several methods of producing sesamol from heliotropin as a starting material are known. For example, the following methods are disclosed:
(1) reacting heliotropin with hydrogen peroxide in methylene chloride serving as a solvent and in the presence of caustic soda and a selenium compound (Synthesis, 1989, March, 167);
(2) reacting heliotropin with peracetic acid or hydrogen peroxide in methylene chloride serving as a solvent (J. Org. Chem., 1984, 49, 4741 and Sekiyu-gakkai shi 29, (5), 364 (1986));
(3) reacting heliotropin with chloroperbenzoic acid in methylene chloride serving as a solvent (Ind. J. Chem., 1983, 22, 1150);
(4) reacting heliotropin with performic acid in chloroform serving as a solvent (USSR Patent No. 688492); and
(5) reacting heliotropin with peracetic acid in ethyl acetate serving as a solvent (Japanese Patent Application Laid-Open (kokai) No. Heisei7-25868).
The aforementioned method (1), which employs a highly toxic selenium compound, is difficult to carry out on an industrial scale. Methods (2) to (4) are also difficult to carry out on an industrial scale, since these methods employ a halogen-containing solvent, whose use as been discouraged in recent years due to environmental impact.
Although the aforementioned method (5) is advantageous in that it can be carried out in ethyl acetate (i.e., a chlorine-free customary solvent), generation of a large amount of heliotropic acid, which is a by-product difficult to dissolve in most customary solvents including ethyl acetate, requires an alkali-extraction step, thereby making the production steps cumbersome.
Specifically, Japanese Patent Application Laid-Open (kokai) No. Heisei7-25868xe2x80x94related to method (5)xe2x80x94discloses a step of producing sesamyl formate by oxidizing heliotropin with peracetic acid in a specific organic solvent and in the absence of water; a step of producing sesamol by hydrolyzing the ester, without separation of the ester, in the presence of a base or water; and a step of obtaining (purifying) sesamol by separating the organic layer formed during the hydrolysis from the aqueous layer and subjecting the organic layer to distillation. Since this method produces a large amount of heliotropic acid as a by-product, the hydrolysis mixture is subjected to phase-separation so as to dissolve the by-product in the formed aqueous layer for removal thereof.
Increase in by-product yield of heliotropic acid reduces the yield of sesamol and generates solid deposits, to thereby render handling of the reaction mass difficult.
The present inventors have carried out extensive studies so as to solve the aforementioned problems, and have found that the by-product yield of heliotropic acid can be remarkably reduced by oxidizing heliotropin with peracetic acid in the presence of formic acid. The present invention has been accomplished on the basis of this finding.
Accordingly, an object of the present invention is to provide a method of producing sesamol with high efficiency.
In one aspect of the invention, there is provided a method of producing sesamyl formate, which comprises oxidizing heliotropin with a percarboxylic acid in the presence of formic acid and an optionally added organic solvent.
Preferably, the yield of by-produced heliotropic acid is 5 mol % or less.
Preferably, formic acid is added in an amount of 25-500 wt. % based on 100 wt. % of heliotropin.
Preferably, the percarboxylic acid has 1-7 carbon atoms.
Preferably, the organic solvent is a C1-C7 carboxylic acid; a C1-C6 alcohol ester of a C1-C7 carboxylic acid; or a mixture thereof.
In a second aspect of the invention, there is provided a method of producing sesamol, which comprises decomposing, by adding water and/or alcohol, sesamyl formate obtained through the aforementioned method of producing sesamyl formate.
Preferably, sesamyl formate is decomposed in the presence of a basic catalyst.
Preferably, the catalyst is removed after decomposition; a low-boiling-point substance is separated; and, successively, sesamol is collected through distillation.
Preferably, the catalyst is allowed to remain after decomposition; a low-boiling-point substance is separated; and, successively, sesamol is collected through distillation.